In modern society, cardiovascular diseases originating from arteriosclerosis are increasing with changes in lifestyle and aging. However, medical care systems for early detection of these diseases are still undeveloped. Evaluation on the softness of blood vessel walls is very important for diagnosis of arteriosclerosis. At the present, image diagnostic methods by the use of MRI's and X-ray CT scans, and pulse wave velocity method are generally adopted for the diagnosis of arteriosclerosis. However, tests with MRIs and X-ray CT scans generally are costly, and these methods are not suitable for daily monitoring.
The pulse wave velocity method is based on the fact that the propagation velocity of the pulse wave changes according to the hardness/softness of blood vessel walls, and this pulse wave velocity method is generally used in medical practice, since a test using pulse wave velocity method is easy to conduct and also convenient. However, the relationship between age and pulse wave velocity is indistinct, and the accuracy of the diagnosis by this method is regarded as low, especially from the standpoint of prevention and in view of individual differences.
Japanese Patent Laid-Open Publication No. 2004-113593 proposes an apparatus including a pulse wave detection device to be attached to a specified site on a living body, and a compression device disposed downstream from the pulse wave detection device to suppress the blood flow by compressing another site on the living body. While the compression device is suppressing the blood flow, the pulse wave detection device detects the peak of a traveling wave component of the pulse wave and the peak of a reflected wave component of the pulse wave, and the apparatus evaluates the degree of arteriosclerosis based on the detection results. More specifically, a cuff incorporating a first compression bag and a second compression bag is attached to an upper arm, and, while the blood flow is stopped by the second compression bag, the upper arm pulse wave is detected by the first compression bag. This upper arm pulse wave is a synthetic wave of the traveling wave and the reflected wave that is generated at the site where the second compression bag is attached. The harder the artery is, the greater the reflected wave is, and the faster the speed of the reflected wave is. The time difference between the peak of the traveling wave component and the peak of the reflected wave component and the intensity ratio of these wave components to each other are calculated by use of an artery hardness calculation means. From the facts above, the calculated time difference and intensity ratio depend on the hardness of the artery, and it is considered that evaluation of the degree of arteriosclerosis is possible in this way.
Japanese Patent Laid-Open Publication No. 2006-158426 proposes another apparatus for evaluating the vascular function. For example, a first pulse wave detection device is attached to an upper arm, and a second pulse wave detection device is attached to a knee. Supposing that the time from a rise to a peak of the pulse wave of the elastic artery detected by the first pulse wave detection device is tp1 and that the time from a rise to a peak of the pulse wave of the elastic artery detected by the second pulse wave detection device is tp2, the time tp1 is almost equal to the time tp2 in normal cases. However, if the subject has arteriosclerosis, the peak of the pulse wave detected by the second pulse wave detection device comes earlier, and if the subject has arterial obstruction, the peak of the pulse wave detected by the second pulse wave detection device comes later. It is considered that evaluation of the vascular function is possible in this way.